The present invention relates to a grease composition which has improved rust prevention and abrasion resistance properties.
Extreme pressure greases have many uses, because of their excellent abrasion resistance and their ability to withstand loads, for example in bearings and gears in the automobile, iron and steel, railway, and various other, industrial mechanical devices.
Typical extreme pressure grease compositions are in general those which contain, in various types of grease, additives such as olefin sulphides, sulphides of fats and oils, sulphur-phosphorus-based extreme pressure agents, molybdenum disulphide, organomolybdenum compounds, lead compounds and zinc dithiophosphate.
Recent art has disclosed grease compositions containing sodium thiosulphate, which have excellent extreme pressure properties: in the Specifications of Japanese Laid-open Patent 3-131690, Japanese Laid-open Patent 11-35965 and U.S. Pat. No. 4,923,625.
However, the abrasion resistance in these prior art documents is unsatisfactory and there is the further possibility that rusting will be induced because sodium thiosulphate has the property of absorbing moisture. In particular, since bearings and gears of steel equipment and foodstuff machinery are lubricated under conditions where there are large quantities of water, the production of rust is promoted and problems with respect to lubrication are readily produced.
It is therefore highly desirable to be able to provide grease compositions in which the extreme pressure properties of grease compositions which contain sodium thiosulphate are retained well, whilst the production of rust is inhibited and abrasion resistance is also improved.
The present invention provides a grease composition comprising a base oil and a thickener, which grease additionally comprises from 0.05% to 30% by weight of sodium thiosulphate and at least 0.1% by weight of one or more additives selected from the group of: calcium salicylate, magnesium salicylate, calcium phenate and/or calcium sulphonate, based on the total grease composition.